Acoustic black hole with functionally graded perforated rings and sound absorbing layers: Theory and experiments

This paper presents a theoretical and experimental study of the acoustic characteristics of a class of Acoustic Black Hole waveguides (ABH) with Functionally Graded Perforated Rings (FGPR) which are sandwiching Sound Absorbing Layers (SAL). This class of ABH has enhanced energy dissipation characteristics derived from the simultaneous flow through the perforations and the sound absorbing layers. With such capabilities, the proposed ABH/FGPR provides rapid attenuation of the propagating waves as it travels along the length of the waveguide. The prediction of the behavior and the optimal design of the proposed ABH/FGPR are carried out using a COMSOL-based finite element modeling (FEM) approach. Numerical simulations are conducted to demonstrate the merits and behavior of various favorable configurations of the proposed ABH. The predictions of the FEM are compared to validate their accuracies. The theoretical predictions are further validated against experimental results using the ACUPRO impedance tube. Comparisons between the predictions and measurements reveal close agreements. Furthermore, the obtained results emphasize the importance of using SAL in extending the energy absorbing characteristics of the proposed ABH/FGPR over broad frequency range even with fewer number of rings.